[vonBaloney]

In all the years I've seen that question asked in forums, I don't recall one time when it wasn't actually a question about format equivalence. Usually it's asked because the poster has seen discussions about the subject, but is unaware of the concept of equivalence.

They can't be asking about equivalence if they've never heard of it. It isn't really about equivalence -- it is "what's this all about"?

Exactly. If the question comes up it's because they are seeking further explanation, and "a lens doesn't change properties, period" just doesn't help them understand anything better when it's not accompanied by some very basic info about format equivalence. I seen it actually mislead folks, giving them the impression that lenses bring exactly the same image no matter what format camera they put them on.

I think what they need to know is that they are getting a bigger or smaller crop of the same unchanged image. Talking about equivalence almost always confuses that point and still makes it sound like the lens does something different on a different body. To me, the wikipedia photo on "crop factor" clarifies the issue perfectly:

[bossa]

It's not unchanged if the crop is habitually enlarged to the same sizes as the FF would have output to as everything about the image is magnified comparatively. My computer monitor doesn't get bigger just because I'm using a FF.

[jsherman999]

They can't be asking about equivalence if they've never heard of it. It isn't really about equivalence -- it is "what's this all about"?

No, No, No, that's my whole point - they are usually asking about equivalence, they just don't know to use the word. Or, more accurately, the question they ask is best answered with some basic information about equivalence. (and you don't even need to use the word 'equivalence' in the answer if you don't want, just relay the concept descriptively. )

I think what they need to know is that they are getting a bigger or smaller crop of the same unchanged image. Talking about equivalence almost always confuses that point and still makes it sound like the lens does something different on a different body. To me, the wikipedia photo on "crop factor" clarifies the issue perfectly:

Except for the DOF-for-same-FOV issue. If they don't ask about the lens's aperture as part of the question, just sticking to the equivalent crop factor is probably sufficient, though, if you're in a hurry.


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[vonBaloney]

It's not unchanged if the crop is habitually enlarged to the same sizes as the FF would have output to as everything about the image is magnified comparatively. My computer monitor doesn't get bigger just because I'm using a FF.

I really don't understand this talk about enlarging a crop and having it change -- the DOF doesn't change, nor does anything else -- everything is just relatively larger, rescaled. People are making it sound like choosing a different print size will somehow affect the basic optical qualities of the photo.

[vonBaloney]

No, No, No, that's my whole point - they are usually asking about equivalence, they just don't know to use the word. Or, more accurately, the question they ask is best answered with some basic information about equivalence. (and you don't even need to use the word 'equivalence' in the answer if you don't want, just relay the concept descriptively. )




Except for the DOF-for-same-FOV issue. If they don't ask about the lens's aperture as part of the question, just sticking to the equivalent crop factor is probably sufficient, though, if you're in a hurry.


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All I know is that once upon a time I was one of those asking these questions and if you had just showed me that picture with the two boxes that would have been the end of it. Talking about all this equivalence stuff would have led to a long back and forth and when you finally just said -- "it's cropped, that's it" or showed me that photo I would have said, "Well why didn't you just say that in the first place?"

[jsherman999]

All I know is that once upon a time I was one of those asking these questions and if you had just showed me that picture with the two boxes that would have been the end of it. Talking about all this equivalence stuff would have led to a long back and forth and when you finally just said -- "it's cropped, that's it" or showed me that photo I would have said, "Well why didn't you just say that in the first place?"

Because a 300 f4.5 lens shot on FF is equivalent to a 200mm f/2.8 lens shot on aps-c - not a 200 f/4.5 lens. You should probably mention the entire effect, not just the FOV change.

[vonBaloney]

Because a 300 f4.5 lens shot on FF is equivalent to a 200mm f/2.8 lens shot on aps-c - not a 200 f/4.5 lens. You should probably mention the entire effect, not just the FOV change.

The point I was making is that if it were being explained to me I wouldn't want to hear about equivalent lenses at all -- it is very confusing to talk about that until you understand the effect you'll get using the SAME lens on a camera from each format. Once I understand that (which is very simple -- "it's cropped, period"), I don't need to have the the equivalence stuff explained (or it would make it much easier anyway) because it all follows logically and is perfectly clear.

Going straight to "how to get the same effect using different lenses on different formats" is way more confusing without the foundation of knowing what happens with the same lens on those different formats because that is immediately where the mind goes for a newbie, e.g. "Hey I heard that if I use a 300mm I'm really getting a 450mm, is that true?" and the simple answer is "No, you're getting a cropped 300mm". THEN you mention that because the smaller sensor has probably got a better resolution per-square-inch than a larger sensor, it is somewhat like having a 450mm on an FF if it is a good lens, etc etc. And then you can talk about DOF differences and how to get equivalent effects.

But it all starts with "it's cropped, period". Because without understanding that then the rest will be mud. Again, speaking from my own experience. That is what made it click for me and then I realized it was much ado about nothing.

[Class A]

People are making it sound like choosing a different print size will somehow affect the basic optical qualities of the photo.

The point is that producing the same print size from different negative/sensor sizes results in different optical qualities (e.g., DOF). The whole "equivalence" notion is not an overcomplication; just stating "the properties of the lens don't change" or "just the AOV changes / it is just a crop" is not sufficient.

[vonBaloney]

The point is that producing the same print size from different negative/sensor sizes results in different optical qualities (e.g., DOF). The whole "equivalence" notion is not an overcomplication; just stating "the properties of the lens don't change" or "just the AOV changes / it is just a crop" is not sufficient.

It was sufficient for me as I keep saying. All this other nonsense is needlessly confusing. Start with the simple -- the one with less variables. Same lens/different formats (one fixed variable) is much less complexity to talk about than different lenses/different formats (no fixed variables), and so the former should be tackled before the latter. What is sufficient to understanding is up to the student, not the teacher. I'm just saying first things first.

[eddie1960]

It's not unchanged if the crop is habitually enlarged to the same sizes as the FF would have output to as everything about the image is magnified comparatively. My computer monitor doesn't get bigger just because I'm using a FF.

now you get into different territory. theoretically if both cameras have the same number of pixels the FF will not be as good if cropped to the apsc crop. for the ff to have the same large printability as a 16mp apsc it needs to be 30 mp (so the D800 will actually be better when it arrives)

I was selling when the stupid Crop explanation was arrived at. it was in many ways a poor way of explaining the difference to long time film users, but we generally wanted to keep it as non technical as possible.

It's handy to visualize what the lens will show on a different body if you are well versed in how it would have looked on film or FF. If you are not (like most people BTW) then it is just added confusion.

I do realise the DOF will be different all things considered, but they again it's different on my 645 and 6x7 as well at the same aperture

[bossa]

I really don't understand this talk about enlarging a crop and having it change -- the DOF doesn't change, nor does anything else -- everything is just relatively larger, rescaled. People are making it sound like choosing a different print size will somehow affect the basic optical qualities of the photo.

This is how I see this: Perspective is a spatially relative perception that takes into account the entire image circle of a lens' projection whereas a central crop ignores the closer (side/up/down) parts of the image. Magnifying a central portion of an image's perspective 'flattens' the form as it removes other relevant and relative visual information. After you enlarge that the extra little bit to satisfy your viewing requirements it is a multiple of the crop factor and as such changes relative aspects of the image.. i.e. DOF. Nothing has really changed, in a way, but the scale of the viewing situation relative to your own physical size and eyesight resolving power. The reason it is so hard to understand is because it is not an absolute quantifiable effect.

[vonBaloney]

This is how I see this: Perspective is a spatially relative perception that takes into account the entire image circle of a lens' projection whereas a central crop ignores the closer (side/up/down) parts of the image. Magnifying a central portion of an image's perspective 'flattens' the form as it removes other relevant and relative visual information. After you enlarge that the extra little bit to satisfy your viewing requirements it is a multiple of the crop factor and as such changes relative aspects of the image.. i.e. DOF. Nothing has really changed, in a way, but the scale of the viewing situation relative to your own physical size and eyesight resolving power. The reason it is so hard to understand is because it is not an absolute quantifiable effect.

You're confusing me even now. It is not like people are actually carrying around cameras of both formats with a huge bag of lenses and trying to figure out how to mimic the effect of one with the other. If someone has an APS-C, all they are going to see is what that format gives them. You make it sound like they need to be saying to themselves as they look through the viewfinder, "Ok, I must remember that the perspective is flattened here compared to some other thing I don't have. I'm losing visual cues and the effect that I have here is different than that other thing. Must remember that. I don't know why, but I must." It's crazy. The difference between the two is that one is a cropped version of the other. THAT'S IT! That's the only difference, and everything else you guys are talking about is a logical consequence of that difference, but would only be relevant to that mythical person walking around with both formats and a big bag of lenses. Why in the world would a newbie need to hear about the *subjective* flattening of perspective (since it isn't really) compared to a format they don't have? That's going to make things clearer? Again, if you want to go there, that's fine, but I don't understand this resistance to starting out with a simple explanation of the ACTUAL technical difference between the two (one is a cropped version of the other). Until someone "gets" that, they have no hope of understanding the rest of this stuff that apparently they must be told or they'll be lost.

In real life, the difference only really matters when you are picking out a camera to begin with because you do have a choice now. And then what you need to know is for wide-angle stuff, you *might* have an easier time with FF because you have more lens choices. And *maybe* APS-C will be a bit better for telephoto because of the price/performance ratio of the resolution you're getting. Along with other considerations of available lenses, size and handling of the body, etc etc. But no one needs to think about "equivalence" when they are actually working with whichever format. And if someone is buying a FF, all this stuff wouldn't even be mentioned. No one says, "the perspective is unflattened with the camera because of the reverse crop factor".

[Doanh]

+1 to vonBaloney. This is how I understand. Simple, uncomplicated.

Respectfully,

Peter

You're confusing me even now. It is not like people are actually carrying around cameras of both formats with a huge bag of lenses and trying to figure out how to mimic the effect of one with the other. If someone has an APS-C, all they are going to see is what that format gives them. You make it sound like they need to be saying to themselves as they look through the viewfinder, "Ok, I must remember that the perspective is flattened here compared to some other thing I don't have. I'm losing visual cues and the effect that I have here is different than that other thing. Must remember that. I don't know why, but I must." It's crazy. The difference between the two is that one is a cropped version of the other. THAT'S IT! That's the only difference, and everything else you guys are talking about is a logical consequence of that difference, but would only be relevant to that mythical person walking around with both formats and a big bag of lenses. Why in the world would a newbie need to hear about the *subjective* flattening of perspective (since it isn't really) compared to a format they don't have? That's going to make things clearer? Again, if you want to go there, that's fine, but I don't understand this resistance to starting out with a simple explanation of the ACTUAL technical difference between the two (one is a cropped version of the other). Until someone "gets" that, they have no hope of understanding the rest of this stuff that apparently they must be told or they'll be lost.

In real life, the difference only really matters when you are picking out a camera to begin with because you do have a choice now. And then what you need to know is for wide-angle stuff, you *might* have an easier time with FF because you have more lens choices. And *maybe* APS-C will be a bit better for telephoto because of the price/performance ratio of the resolution you're getting. Along with other considerations of available lenses, size and handling of the body, etc etc. But no one needs to think about "equivalence" when they are actually working with whichever format. And if someone is buying a FF, all this stuff wouldn't even be mentioned. No one says, "the perspective is unflattened with the camera because of the reverse crop factor".

[jsherman999]

... But no one needs to think about "equivalence" when they are actually working with whichever format. And if someone is buying a FF, all this stuff wouldn't even be mentioned.

IMO, it would be silly not to mention it to someone thinking of spending the money to get a FF camera, because for some it's an important selling point.

[Jüri]

The difference between the two is that one is a cropped version of the other. THAT'S IT!.

I don't acutally think it's that simple. Because the edges of APS-C are cropped compared to FF, in order to take similarly composed photo with a APS-C you'll have to move further from the subject. And that will alter DoF, perspective, angle etc.

But no one needs to think about "equivalence" when they are actually working with whichever format.

I'm not sure I understood what you mean, but equivalence makes a lot of difference to me. A 28mm lens is very wide on my FF camera, but almost normal focal length on APS-C. So that's something I always need to consider when choosing what to use.